O21 West Essex Highlands Geotech Slope Stability Model Memo 20250812pdf

Princeton Hydro, LLC Page | 4 Sensitivity Analysis of Geologic Strength Index (GSI) As I previously testified, a weak rock mass, particularly in the northeastern area of the site, was indicated by the low Rock Quality Designation (RQD) values. A Geological Strength Index (GSI) value reflective of the poor and very poor joint conditions, common in heavily fractured rock, should be considered. A ten-foot-thick layer of bedrock with weaker parameters was added to the models below the decomposed bedrock layer to represent the 10 feet of rock coring performed during the soil borings. Model trials of Cross Sections C and D were evaluated with a GSI value of 20. The other rock material properties selected by Langan were maintained to inform this sensitivity analysis. Figures 3 and 4 below provide a zoomed view of the potential failure surfaces with factors of safety below 2.0 for both cross sections. Figure 3: Cross Section C with Bedrock Layer of GSI=20